In this scenario – who is in the wrong ?

21 Oct, 2020

I know these situations happen all the time – BUT who is in the wrong on this one ? …. the customer or the airline .
Flight booked with connection internationally and domestic bookings…
Outward bound –
Stage 1 :Domestic flight to international terminal all fine … at this next stage 2 the next flight being international departure announces a delay due to technical difficulties of the aircraft causing delay , delay extended again then the problem solved & flight proceeds. During the delay the customer advises this airline that they have a connecting flight that they may miss now?
Airline advises that due to the boarding passes being issued from outset of the journey ..the associate airline will be informed that this delayed flight will have the customer on board its flight – and as long as customer makes it to the departure gate of the associate airline before departure all will be ok…. customer arrives within 10 minutes of departure of stage 3 flight – manages to have staff of associate airline allow their luggage to be placed on board the plane and customer sent thru to board the plane to find their seat. BUT at this stage the flight staff state ” Wait – what about the stand bys now allocated to that seat? “
Would they ( the stand by customer ) be the one removed or would it be the original customer who booked this flight 6 months ago ? & thru no fault of their own the delay in catching that flight was out of their control.
Should the responsibility not have been with the airline to ascertain if that client was on a connecting flight ? & if the delay of connecting flight could cause delay to that ticket holder not being able to check in on time ?? Therefore dont allocate that one as a stand by seat wouldnt you think ?
​Your thoughts please ?